text:
"Airplane mode" does not disable GPS... is it safe to use GPS in flight?
I noticed that even when my phone is in "airplane mode", I can still use the GPS.
Theoretically a GPS receiver just receives data, so I guess it would not jam anything.
On the contrary, on the iPhone airplane mode disables GPS, so it means that at least a few engineers at Apple are worried about people using GPS in flight.
Is it really OK to use my phone's GPS in plane, as a passenger of a typical commercial flight?
(when use of electronic device in airplane mode is allowed, obviously)

What model of phone do you have? On iPhone, the GPS is disables in airplane mode: http://support.apple.com/kb/ht1355

@Floris: Interesting! I have a Huawei GLS07.

A lot of people use 'Airplane mode' as 'Power saving mode'. It's possible that Apple turns off the GPS to save power.

@daviewales seems plausible. They're rather strict (to the point of being anal) about power consumption requirements of apps submitted to their appstore as well.

on my Android phone, to get GPS in airplane mode i have to first turn on airplane mode, which turns off GPS, then turn GPS back on.

theoretically? GPS IS receive only. There's no way to talk to the GPS satellite network except using the big antennas of the network owners (the US DoD) and the communications are no doubt heavily encrypted.
Now, does that mean it's "safe" for aircraft electronics. Any receiving antenna does have an EM field around it, so if you believe the myth that those electronics are so sensitive and easy to jam that any EM field at all causes them to malfunction the answer is an obvious NO.
But that myth is just that, a myth. If they were so sensitive, that old walkman you were using in the 1980s during flights would have brought down that aircraft. Because not only do antennas have EM fields around them, any electrical device that's turned on has one (in fact any electrical cable with a current flowing through it has one, including the headphone cord for the in flight entertainment system).
And that GPS system in your cellphone uses a lot less power than that walkman, has a far weaker field surrounding it.
Of course it's theoretically possible that a strong enough EM field might interfere with the electronics in an aircraft, but then to you'd need just the right signal. Which would indicate you need intent (or incredible bad luck)!
Effectively the GPS in your cellphone is a lower powered version of the GPS receiver in the belly of the aircraft, which has its own antenna (which no doubt has a similar field around it, but of higher strength).

there are different frequency bands for each of your mentioned examples and some electronics are more sensitive to some frequencies

@ratchetfreak yes, but still holds that the energy levels are not nearly enough to cause interference. If they were, just flying through the reception area of say a cellphone tower would cause an aircraft to crash. Or taking off over a neighbourhood where someone's got his television turned on. Haven't heard of either in years, or ever for that matter.

A receiving antenna interacts with EM propagation around it... but does so even when unpowered.  Turning GPS "off" wouldn't eliminate interference caused by signals diffracting, refracting, and reflecting off elements of the GPS receiver.

@BenVoigt true, was thinking more of the standing EM field that is present around any powered up electrical circuit (a field that's usually weak enough it's of no consequence to the end user, but designers may have to take measures to attenuate it to prevent interference between components).

Also of note, many GPS chipsets will automatically disable themselves when travelling over a certain speed over a certain height. This is to prevent their usage in the guidance system of an Unmanned Aerial Vehicles, which during the time this decision was being made, included only Cruise Missiles.

@Aron: No, Cruise Missiles aren't covered. You're confusing them with ICBM's. IIRC the legal limit is something like 30.000 feet and Mach 1, but some GPS vendors incorrectly took that as 30.000 feet or Mach 1.

@MSalters more likely IRBMs, the Scuds and similar of the world. Countries capable of building ICBMs aren't going to need to mount civilian grade GPS receivers for their warhead guidance systems ;)

@jwenting MSalters is spot on. Even state-of-the-art inertial navigation have worse accuracy over 6000km than customer-grade GPS. 1Mach/ 30kfeet was implemented precisely to stop Russkis from getting better bang out of their nukes. BTW, countries that have IRBMs also have ICBMs.

@Agent_L some of them, not all. Until recently Germany had IRBMs for example in the form of Pershing 1 missiles. Iran has IRBMs in the form of Scud (and derivatives), a weapon that's been exported widely to Soviet satellite states (and in its derivative forms built in Iran and North Korea, among others, to other countries still). None of those have ICBMs. Israel has IRBMs of its own design, no ICBMS. So does India (though technically their space launchers could be pressed into service as such). The list goes on and on. Germany in fact designed the first IRBM in the form of the V2 in the 1940s.

Decades before the first ICBM was created. Other countries followed suit (UK, USA, USSR, France, etc.) quickly.

@jwenting Those are short range (SRBM), not intermediate (IRBM). India eventually developed their IRMBs into ICBMs too.

@Agent_L not really. Both Iran and Israel at the very least have created their own IRBMs (thousands of KM range). North Korea has almost certainly done the same (probably in cooperation with Iran tbh). Your statement that having IRBMs means that you instantly also have ICBMs is the problem, not that IRBM development is often a precursor to ICBM development (though it doesn't have to be, India doesn't have ICBMs, they don't need them. No doubt their space launchers could be reconfigured as such but AFAIK they haven't been. India has SLBMs and IRBMs to strike Pakistan and China).

@jwenting Yeah! 5 comments nitpicking over side remark over class that has been deprecated. I agree with you about Iran and Israel, but you're wrong is many other points: Classifying short-range V2 as IRBM (A9 never left drawing boards). Indian Agni5 is certainly not mass produced yet, but they're launching them since 2012, no need to hack space launchers. The problem is your statement that having ICBMs instantly gives access to inertial guidance better than GPS, while best American and Russian ICBMs as of 2016 achieve their accuracy exactly by incorporating GPS/GLONASS reference.

Bombs aside, it's NOT a myth, and in fact Walkman devices have been reported to cause problems. Also there was one famous case of a cd player interfering with the ILS receiver in an airliner on final. The indicated radial was off by a full 20 degrees when the cd player was turned on, and 0 when turned off. The pilot had to hand fly the approach to keep the autopilot from veering off course. Electronic devices do not have to have an intentional radiator to generate RF. That is why part 15 FCC rules exist. Source: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960009442.pdf

@Bill unless you talk using the same frequency band, or a harmonic wit the frequencies used in communication by the aircraft. being "active" or "not active" doesn't matter for the aircraft: even inactive you interact as you're still an antenna - creating noise, the only way this could be fixed is if the antenna is physically cut into many pieces, I don't see phones doing that.  Talking on the same frequency or a harmonic can indeed decrease the effective bandwidth of other communicating devices. But doesn't aviation use their own bands?

@paul23 my point is that it doesn't even have to be a transmitter to have an rf emitter on unknown frequencies. The case I mentioned was a CD player which has no transmitter at all. Also, modern superheterodyne receivers have multiple intermediate frequencies which convert the signal along the way. In other words, there is no telling. Legally, if the captain says no, the answer is no, with very few exceptions (pacemakers, tape recorders, electric shavers, and hearing aids).

"It depends".  As others have mentioned, GPS is receive only.  In theory at least, when everything is operating normally.  In practice, some GPS units can fail in a way that causes them to become an unintentional radiator of energy.  GPS signals are VERY weak, so it doesn't take much to jam them.  However, this should be an exceptionally rare event, and terribly unlikely to happen with integrated handheld devices.   My personal GPS unit failure experience:
I was flying a light twin (Piper Twin Comanche) with a Garmin 430 WAAS onboard and an iPad with EFB/position tracking software.  All of a sudden both of them lost GPS signal.  Eventually through trial and error we found that turning off the onboard (certified) Garmin 430W restored the iPad, but not the other way around.  Upon landing we gave the airplane over to the maintenance crew who discovered that the antenna cable to the Garmin was damaged.  Apparently it uses an amplified antenna, which when the cable became damaged turned into an incidental transmitter and jammed the GPS signal around us!

Confirmed in two cases in my personnal experience. I work as a hydrographic survey engineer, and fit GPS units on ships on a frequent basis. I have twice found faulty GPS units that have had antennae fail in such a way as to become low-power transmitters. Althought GPS units are technically recieved only, they use a powered phased array antenna design, which can radiate in certain failure cases.

Anecdotes like these are precisely why there were always such strict rules about electronics on planes - the concern is more with malfunctioning electronics than the ones that work properly. Glad you were able to figure this one out - and that you found your way home on that occasion.

It was a bit more annoying than usual as it was night time, but we knew roughly where we were anyways, so we just flew home based one the locations of the city lights.  We had functioning VOR receiver on board and worst case could have shot the VOR approach to put us on the runway.  Failing that, the local TRACON has radar out to where we were, could have called them up too.  Aviation is full of backup plans.  :-)

Technically speaking, all GPS units are unintentional radiators of energy. The questions are just how much energy and at what frequencies. Good answer, though. +1 Good point regarding the weakness of GPS signals, too. Most people don't realize it, but GPS received signals are incredibly weak. They're typically on the order of hundreds of attowatts, around -127 dBm.

"Receiving only" is the same as "transmitting", since signals are broadly zero power  there is no "stronger field" when you transmit - or passively exist in a changing field (which anything is by now, unless you go deep underground to where they detect neutrinos you're in a heavily changing EM field, which your metal will interact with). - And unless the conductivity is infinite the resistance will make an interference with the signal. - You just have to be sure not be in a harmonic oscillation, but that depends on physical properties, not "on" "off" configuration.

The regulations on a plane used to forbid the use of any devices capable of sending radio signals - whether deliberately, or accidentally. Most radio receivers contain several "intermediate frequency" stages, where the incoming frequency is mixed with a "local oscillator" to produce lower frequencies which are easier on the electronics. These local oscillator frequencies have a tendency to "escape" from the receiver - but on GPS in particular, the amount of signal thus emitted is very small, and the frequencies are "mostly harmless".
A very helpful site on this topic is http://gpsinformation.net/airgps/gpsrfi.htm . The most important sentence (IMO) from this site is

The interference potential of handheld GPS receivers is minimal.  However,  no passenger should EVER operate a GPS receiver on board an aircraft except in strict accord with the directives of the flight crew.

It also has an extract of FAA regulation 91.21 . I found the original at the ecfr website (I added some emphasis):

§91.21   Portable electronic devices. (a) Except as provided in
  paragraph (b) of this section, no person may operate, nor may any
  operator or pilot in command of an aircraft allow the operation of,
  any portable electronic device on any of the following U.S.-registered
  civil aircraft:
(1) Aircraft operated by a holder of an air carrier operating
  certificate or an operating certificate; or
(2) Any other aircraft while it is operated under IFR.
(b) Paragraph (a) of this section does not apply to—
(1) Portable voice recorders;
(2) Hearing aids;
(3) Heart pacemakers;
(4) Electric shavers; or
(5) Any other portable electronic device that the operator of the
  aircraft has determined will not cause interference with the
  navigation or communication system of the aircraft on which it is to
  be used.
(c) In the case of an aircraft operated by a holder of an air carrier
  operating certificate or an operating certificate, the determination
  required by paragraph (b)(5) of this section shall be made by that
  operator of the aircraft on which the particular device is to be used.
  In the case of other aircraft, the determination may be made by the
  pilot in command or other operator of the aircraft.

Notice - the FAA basically does not have the final say - they say "if the operator determines it is safe, then go ahead". Conversely, if the carrier doesn't say it's safe, you are actually breaking the law by doing this.
So you will need to check with the operator of the flight. For example, Delta explicitly allows the use of portable GPS from gate to gate:

You may use the following devices from gate to gate on Delta and Delta Connection flights:

AM/FM or satellite radios
digital and video cameras
calculators
Delta-installed equipment such as in-flight entertainment systems
DVD players*
e-readers
electric shavers
electronic/digital watches
global positioning system (GPS) receivers
handheld computer games
headphones
laptop computers*
medical devices**
noise reduction headphones
portable media players*
pagers
smartphones and any device with cellular network service must be turned off or in airplane mode
tablets and wireless keyboards or mouse

I was surprised to see wireless keyboards in this list. These are devices that are designed to transmit radio signals - admittedly Bluetooth is low power, but it shows that airlines have actually gone from a blanket "no way" to doing the measurements needed to prove that these things are safe. Either that, or they are reckless in an attempt to attract customers. Let's hope it's the former...

"from gate to gate" means flight+taxi+enter/exit?

@NicolasRaoul - yes it does. It means "any time". Note that I have encountered different "rules" for the same airlines in different countries: the above are just FAA (which is the US authority).

Requests to the tower to turn off high-power transmitters, (like radar and VHF), during takeoff and landing would not be well-received:)

+1 for the mention of EMI from LOs. I can speak from experience in saying that this is a pain to get rid of, even on receive-only devices. We go to great lengths to keep that stuff quiet because it interferes with our own receiver, but most electronics manufacturers couldn't care less because it's usually outside the frequency ranges they care about receiving accurately (if their device is even trying to receive anything at all.)

Good answer, the best IMHO. The only significant way for a receiver to start radiating is wen the local oscillators used for IF and PLL are somehow connected to "the antenna". But the energy in the LO is so limited that any device vulnerable to it would be a very unreliable design, and would not be allowed in aircraft. There are unsuspected oscillators in so many devices (e.g. clocks or car remote controls) that radio receivers are just ones of many non harmful devices. This fear about electronic devices in planes is a useful urban legend to avoid digging seriously into the question.

@mins -- the mixer is supposed to prevent LO signals from reaching its RF port.  Some old/cheap (unbalanced) mixer designs just aren't that good at that though, and without a preamp in the way, this can lead to RFI due to LO re-radiation by the antenna.  Modern balanced mixers (which will be found in any IC and most discrete-part RF frontends) can achieve LO-RF isolation in the 40-60dB range, and will often guarantee at least 20-30dB isolation.

I can understand the exemptions for heart pacemakers and hearing aids that are more-or-less essential for the continued safe operation of their owners, but electric shavers?  When has that need been so urgent it can't wait until terra firma?  Or am I missing something that the community of beardless people will correct me on?

@TobySpeight - I sse your point - but you are rushing to a meeting as you come off the plane, then five minutes in the bathroom to get rid of the 24 hour stubble may be just the ticket. It's something that frequent travelers may care about.

Generally GPS is a receive only service and does not transmit. Because of this it is considered safe to use in aircraft as long as the use of electronic devices in general is permitted.
However, from your question it seemed that the whole topic came up because the iPhone turns off the GPS when turning on flight mode. You concluded "it means that at least a few people at Apple are worried about people using GPS in flight.".
I am sure this is an incorrect conclusion.
The reason the GPS is turned off on an iPhone when you turn on flight mode is that the GPS and radio are handled by the same chip in some of the iPhones models and that both services are intrinsically linked on iOS devices. This is not the case for some other smart phones. Specifically:
The GSM iPhone 4 still used the Broadcom BCM4750 which could be turned on separately from the radio, but the CDMA version uses the Qualcomm MDM6600 which has Radio and GPS in one chip and is not discretely powered. The iPhone 4S uses the Qualcomm MDM6610 chip for both. I have not researched the 5 or 5S. For Apple its simply easier to turn off all the stuff on all devices rather than throw in multiple options for multiple devices. On top of that Apple uses assisted GPS (AGPS) which downloads satellite coordinates over the network and reduces the time to get a GPS fix from minutes to a few seconds. This is another reason for apple to turn off both together rather than cripple GPS performance without network.
I hope this clarifies things.

The other answer about the possibility of a failure of the GPS receiver chip are not wrong, but they miss a significant point in the use of GPS in smartphones : A-GPS (Assisted GPS)
In order to compute a position, a GPS receiver needs to know the distance between him and a set of satellites, and the exact position of said satellites.
The satellite precise positions (ephemeris) are supposed to be retrieved with the navigation message broadcasted by the satellites.
This message takes some time to be broadcasted (about 12.5 minutes). Remember the old GPS which required a long time to give the first fix ? This is where it comes from. Because it is inconvenient for the average smartphone user, the A-GPS  has been developped. Instead of waiting to receive the navigation message on the slow GPS datalink, this message is transmitted by the traditional cell-phone network much faster. So the A-GPS requires to query this data on the cell-phone network, which means that the cellphone radio transmitter must be on and transmit, which in incompatible with the "airplane mode".
To make it short :

A-GPS : fast for first postion, requires the cell-phone link to be active, hence to transmit. Incompatible with "airplane mode"
"plain old GPS" : slow for first position, is receive only, compatible with "airplane mode"

Although it is not necessary, Apple apparently chose to disable the plain old GPS if the cell-phone link is off.
EDIT : I have just learned from the wikipedia page that some A-GPS device are not even capable of working in "plain old GPS" mode, the position computation being handled by a distant server access by the cellphone network

Having done this before while in flight (I was trying to see if the GPS would be disabled as I had heard commercial GPS systems are designed to not work after a certain velocity).
I can confirm the following:

It works, but its not as smooth or accurate as the in-flight display. There are many reasons for this - one is that due to the size of the screen and the distance covered (and possibly, the scale), each refresh interval has a large gap. In other words, your phone will refresh, and your pointer/pin on the map will jump around a lot.
It takes a long time to get a fix; I could only get 5 satellites (normally the receiver picks up 8+) - again, due to the speed of the aircraft and the fact that when you are not in airplane mode, other radios are used to approximate your position.
Is it harmful to the overall flight systems? Consider that on an average large airliner, not everyone remembers to turn off their devices, I think having a passive thing such as a GPS running - in the long term, would not be harmful to the electronics of the aircraft. I think an electric shaver that you can use freely would cause more problems.

especially the third... If only 10% of passengers forget to turn their phones off or to airplane mode on average per flight, I'd be pleasantly surprised (I forget myself in more than 10% of flights I take, tend to stuff the phone in my bag before security then get annoyed on arrival that the battery's run out trying to get reception at FL300+).

Taking a long time to get a fix or not getting one at all isnt an issue with the speed. The issue is that you are in a big metal tube and the only holes in that tube for a signal to get through point toward the horizon.  If you put your phone on top of and outside the airplane you'd get a fine signal. Civil GPS does have a speed cutout but it is much faster than civil aircraft operate at.

I think critically that in the post 9-11 era when you aren't allowed to take a bottle of water onto a flight that if it was harmful there is no way you'd be allowed it otherwise somebody malicious might deliberately leave their phone on non-flight mode! ;-)

Regarding point number 3, you're right that the EMI from a GPS receiver would be pretty minimal, but I wouldn't really directly compare it to an electric shaver. EMI from something designed to work at radio frequencies (like a GPS receiver) is going to actually be at radio frequencies. On the contrary, EMI from an electric shaver, while likely of higher magnitude than that of a GPS receiver, will be at a rather low frequency. None of its components operate at frequencies anywhere remotely close to the RF range, so the chance of interfering with something in the VHF range is negligible.

As a side note, it is possible to overload the RF front-end and/or ADC of a receiver with any frequency, but if you've got an electric shaver producing that much EMI, you should probably be more concerned about the effect to your face. :)

In my personal experience GPS only works if you hold your phone very close to the windows and the speed is rather low. I saw the GPS stops working at either a specific speed or a specific altitude. And I think it's a restriction added to those chips to prevent hobbyists (and others) from building GPS guided missiles (and other "fancy" stuff the military has). So you can use GPS, but you'll be disappointed most likely.

Cellphones can affect airplane navigation equipment when not in airplane mode.  This was shown in a 2006 episode of Myth Busters.  In the link, please read the paragraph, this is true even though it says "Busted" on that page. This test was done in reasonably scientific manner and it shows that navigation equipment can be affected.
More recently however PED (Portable Electronic Devices) were deemed safe by the FAA for use during flight.  This includes cellular phones, with the expectation is that phones will be set to airplane mode.  Many devices, including the iPhone and iPad, with GPS functionality are included on this safe list.
GPS, for your cellphone is for the most part a receive only activity.  Your cellphone does not have the power to transmit signals the 22,000+ miles it would need to get to a geostationary satellite in space.  Nor does it need to.  You can read how GPS works here.  Any electromagnetic device turned on will transmit some interference, but there isn't much reason to believe that your phone would add much more interference running with GPS on, versus while it's off.
Interference coming from your GPS antenna should be coming from the frequency 1575.42 Mhz.  This range isn't mentioned on the RF exposure information offered by Apple describing it's iPhones, presumedly because it is negligible.
It's reasonable to believe that having a GPS enabled phone should have negligible impact on a plane's navigation system.

The big question that is raised here is part of the great urban myth of do electronics actually play up with an aircraft's avionics.
My simple answer to your question is if the airline or Pilot in Command has asked you to shut off all electrical devices, there is no exception, it must be turned off.
My realistic answer - I've sat on the phone, flying around using my Bose Headset, and never had an issue. In Australia, there is no law against use of electronic devices except during refueling. Not sure about the rest of the world.

My question is specifically about GPS though... your point is that there is no need to go in "airplane mode" in the first place, am I understanding you correctly?

@NicolasRaoul - The GPS (Receiver or Transmitter) is still an electronic wave, so essentially will have the same effect (if any) on any systems. I'm not sure what kind of phone you have, but when I do switch over to Airplane Mode, GPS is also disabled. May be a glitch with your phone, or something the manufacturer has intentionally done.
Point being though, GPS will have the same effect as mobile or wifi signals.

The second paragraph can be removed, see the last line of my question: "when use of electronic device in airplane mode is allowed, obviously" I am specifically talking about the time when electronics ARE allowed. Thanks!

@JamesHam wrong. There is no such thing as a "GPS transmitter" outside the GPS satellites.

@NicolasRaoul - It refers to the wave length/frequency of the broadcast interferring primarily with the older NDB/ADF (or so I am told). I am also referring to times when electronics "are allowed". As far as I have seen, and the safety briefings I have given, you are asked to turn your phones to Airplane Mode/Off pre-takeoff, and at no point in the flight have I heard "It's now ok to switch your mobile devices back on". So your question itself is a bit twisted?

@JamesHam: Could you please point out how I could edit my question to make it less twisted? Thanks!

As mentioned, I have never had Cabin Crew give me an instruction that it was safe to turn Mobile Devices off Airplane Mode, or On in flight. So "when use of electronic device in airplane mode is allowed, obviously" doesn't really make sense to me?

@JamesHam GPS is not turned off on my Samsung Galaxy S4, when in Airplane Mode.  Interference from the signal once it hits the antenna should be minimal.  Certainly less than the actual signal from the the GPS satellite and probably significantly less than the general EMI emitted by the powered on phone.  Wifi and Cell service will put out much more than the GPS chip.

@JamesHam In the U.S., the ban on cell phone use in flight was never related to EM interference with the airplane in the first place. The ban is from the FCC (which regulates radio transmissions,) not the FAA (which regulates aviation safety.) The ban is due to the fact that cell phones on planes used to cause problems for the cell network, not the airplane. A completely separate regulation (from the FAA) used to ban all electronic devices below 10,000 feet on airliners. That reg was recently removed, but with the caveat that the pilot may tell pax to turn them off for low-vis landings.

Also, it's a bit ridiculous to suggest that aviation regulations would be based on 'urban myths.' Just because you may not understand the reason doesn't mean that there isn't one.

I would have added a comment to @JamesHam's answer but I don't have the rep.
Long story short, Your GPS on your phone is receive only. Yes your antenna will generate some field but I doubt it is much stronger when the phone is on than when it off. (However, antenna and interference were not my area of expertise.)
GPS signals travel at the speed of light. Even plane at top speed is still very close to stationary by comparison to the speed of light. Any issues you have with regards to GPS at speed have to do with your phone's hardware/software.
As far as the safety issue is concerned... It is a myth. Period.
While this is not my area of expertise a little simple logic goes a long way. Consider that your plane is awash in signals at a lot of frequencies while it is on the ground and at landing and takeoff (the most dangerous times). Signals from cell towers, FM and AM radio stations, GPS, DirecTv, lightning, etc. All of these sources bathe the airplane in EM waves across a slew of frequencies. Most bathe airplane with much more power than your phone can. Additionally, every wire with electricity in the airplane puts out an EM signal as well.
Another logic argument, there are approx 200+ people on every major flight in the US. If only 1% forget to turn off our phone that means there are at least 2 people on every flight with their phone's on the entire flight. EM interference happens over the course of less than a second so every hr of flight time represents at least 3600 discrete opportunities for EM interference per operational phone. How many flights crash every day?
Any modern aircraft is digital not analog. So interference due to EM can really only cause a flipped bit or a few. As far as a sweet spot in frequencies is concerned the most likely culprit for interference will come from other aircraft systems that sample and process data at the same frequency as the system being interfered with.
But so what? Every sensor man has ever created will create the occasional bad data point. Planes, satellites, etc all have to be robust to a few bad data points. So every computer that consumes sensor data on airplane has filters built in to it specifically to deal with a short series of bad data points.
Specifically the navigation system is usually blamed when the FAA or someone says EM interference brought that plane down. They then go about telling you how impossible it would be to prove it. So ... why do we believe them?
The navigation system in particular is built in such a way as to cope with missing and bad data. Typically the nav system uses some combination of multiple attitude, acceleration, velocity, and position sensors operating at different update frequencies. GPS is often only updated once a second while gyros and accelerators are updated sometimes 1000s of times a second. Then there is a propagator (or estimator) that calculates the aircraft's position, velocity, and attitude in between GPS updates using the faster sensor data. All of that sensor data is filtered so that the occasional garbage data point (which every sensor ever built generates) doesn't cause the aircraft to behave wildly, unpredictably, and sometimes fatally.
The nav system is often blamed because it is all software and sensors. The engine can't spin up or slow down fast enough for a few spurious data points to cause issues. Neither could the controls surfaces (flaps, ailerons, etc). A spurious blip in the radio or radar by themselves doesn't cause an aircraft to go down. So by deduction it can only be the nav system becoming confused by bad data. Except every modern nav system is inherently robust to noise on the sensor data and the larger the error is in the spurious noisy data the easier it gets filtered out.
Oh, and every single computer system on an aircraft is shielded against EM interference.
EM interference is a boogey man the FAA uses when they don't have an answer. It is reproduce-able in a lab in just the right setting. But the aircraft would never have gotten off the ground if it were sensitive enough to crash due to your cell phone or even 200 cell phones simultaneously in use on board.

"Any modern aircraft is digital not analog. So interference due to EM can really only cause a flipped bit or a few."
This is completely false. ILS is where RF interference is the most dangerous and it's completely analog (and very simplistic analog at that... it's literally just two directional AM signals for the localizer and another pair for the glideslope, almost completely unmodified design since 1929.) Also, VHF/UHF COM radios, VORs, NDBs, etc. are all analog. The on-board computer systems in aircraft are obviously digital, but the radionavigation signals are not.

"Signals from cell towers, FM and AM radio stations, GPS, DirecTv, lightning, etc. All of these sources bathe the airplane in EM waves across a slew of frequencies. Most bathe airplane with much more power than your phone can." This is also false unless you're right beside a cell tower. EM signals degrade with respect to the square of the distance from the transmitter. The received signal from your phone will be orders of magnitude above what's received from any of the sources you mention, except perhaps nearby lightning (which then raises the question of why you're flying near lightning.)

@reirab I'm not sure what class of aircraft you are referring to but if you google "digital ils boeing" I get an ebay listing for digital ILS Receiver from AlliedSignal (a company I once worked for as an engineer). The hardware is listed as being valid for Boeing 737, 47, 57, 67, and 777s. Nothing on the 777 is analog to my knowledge. That said, in my experience, most sensors are analog in nature but converted to digital signals immediately for transmission. I would guess that all the radios you mention are also digital or immediately converted to digital.

@reirab With regard to RF signals at an airport. In most major airports the cell phones I've had always have excellent signal. There is also, typically, at least one ubiquitous public WiFi signal and I'm sure several private ones. Each of significant power. Aircraft fly in or near lightning every day. They used to fly through storms much more often than they do now.

A digital receiver doesn't mean the signal it's receiving uses digital modulation. I'm talking about the ILS signals themselves, not the internal implementation of the receiver/demodulator/user interface. ILS signals are analog no matter what kind of aircraft you're flying because that's what's being broadcast from the ground. They modulate whatever carrier frequency is assigned to that ILS system with 90 Hz and 150 Hz AM with one signal directed to one side of the runway and the other to the other side. The resulting interference pattern tells you your angle relative to the transmitter.

@reirab To address the rest of you comment with regards to power of signals. First, the airport's tower is very close and it uses RF signals (FM I assume) to communicate with aircraft nearby. It also uses Radar to see aircraft nearby. Think that bathes your aircraft in RF of any significant power? For reference, a Wikipedia article on tranmission power: http://en.wikipedia.org/wiki/DBm. It states that a typical FM transmitter provides 100 kW of power at a range of 31 miles (50 km). Your typical cell phone transmits 500 mW.

I'm quite familiar with typical transmit powers, insomuch as I design RF receivers for a living. Aircraft VHF communication radios are AM, not FM. Either way, though, your cell phone is a few feet from the relevant antennas on the aircraft. The tower is usually at least a mile away. More importantly, the tower's radios will be pretty much guaranteed to not be stomping on the ILS frequency (they would fix that real quick if it happened and NOTAM the ILS out-of-service in the mean time.) Consumer electronics aren't supposed to stomp the ILS frequencies, but that doesn't mean they won't.

Remember that signal strength degrades with respect to the square of distance between the transmit and receiver antennas. Thus, close transmitters will be received at much higher power levels than farther away transmitters, even if the farther away transmitter may be using higher transmission power.

@reirab Consumer electronics don't operate in the same frequencies either - not a WiFi transmitter or cell. Am is typically kHz right? WiFi was originally MHz and now almost exclusively GHz. And cell phones transmit in the upper MHz is if remember correctly. You'd have to show me a lot of math before I'd believe that RF leakage from a MHz transmitter would have significant power in the kHz range. Significant enough to penetrate the skin of an aircraft and interfere.

@reirab If I remember correctly, you take the instantaneous power of an omni-directional antenna and evenly distribute it over the surface area of a sphere - thus the radius squared loss. However, the Wikipedia article states that 100 kW is what you RECEIVE at 31 miles NOT the power TRANSMITTED (emphasis not yelling). That 100 kW is what the external aircraft antenna is receiving on a frequency similar to what it uses. Compare that to 500 mW transmitted by your cell phone on a frequency 3 orders of magnitude higher than those radios use.

Modulation scheme and frequency are completely unrelated concepts, except that the signals that are supposed to be used in any given band will typically have a defined modulation scheme. You can broadcast AM at 50 kHz or at 50 GHz, should you so desire. Most aircraft communication and radionavigation systems operate in the VHF and/or UHF bands (hundreds of megahertz.)

If the wiki article says that you receive 100 kW at a range of 31 miles, then it's definitely wrong. That would not only blow every RF front end of any sort for miles around, it would also be quite sufficient to ignite almost anything flammable nearby. I can assure you that it's the transmit power that is 100 kW, not the received power at a range of 31 miles. Typical receive powers even at a range of 10 miles for FM broadcast stations are around -60 dBm (i.e. a nanowatt.)

For an explanation of how ILS works, see this article.

Regarding receiving 'an excellent signal' on your cell or WiFi in an airport, that means you're probably receiving a nanowatt or less. WiFi and cell phones don't usually drop out until the RSSI gets down to -90 dBm or less (i.e. a thousandth of a nanowatt or less.)

I read a couple of other articles after your comment. I assume I misread the first article; 100 kW seems to be an appropriate transmission power. At 31 miles you receive approx 0.01 mW << 500 mW. Thanks for the article on ILS. It appears they use signal power not the interference to determine alignment. Interference would imply phase differencing which should be reasonably robust to random interference. Signal power not so much.


text:
Which jet airliner types have had the fewest accidents per million departures?
Passenger jet transport is very safe, but are there any jet airliners with a lower recorded accident rate?
Edit:
number of accidents per se is of course never a good indicator since it will always rise over the years and with fleet size. Accidents per flying hour skews towards long distance aircraft, since not many accidents happen during cruise. The most objective comparison would be the rate of accidents per million departures of the type.

The question in the header does not match the question in the text.

Yep, fixed it, thx

@mins the number of accidents per million departures seems to be documented well.

All newly developed types have zero number of accidents, at least immediately before the maiden flight.
Hence the actual safety of the type cannot be derived just from the number of the accidents. The number of flights flown must also be taken into consideration. For instance, Concorde used to be the absolutely safe (zero accidents) for many years (1969 - 2000), then it became comparable to other planes just because of the only crash of the type.
This source contains the table that includes the number of airliners operating, not just the number of accidents. It is very incomplete but looks like Boeing 777 and ERJ 135/145 may not be a bad choice while Boeing 737 'Classic' does not look equally good. The safety of this type has been discussed separately.

Accidents per number built....just never use them and they will have a perfect safety record.

accident rate according to your table is utterly meaningless. It doesn't take into account passenger/miles traveled over the period in which the accidents and fatalities are shown. The number currently in service is meaningless as it says nothing about how many aircraft were in operation over time or how much they were used. E.g. the 737 classic used to be far more prevalent but has largely been replaced except in accident prone areas like Africa and parts of Asia where maintenance standards and pilot proficiency tend to be lower.

In any case, it is still better than just to count accidents.

That source is woefully out of date. The 777 has been involved in 3 fatal incidents with hundreds of deaths between 2012 and now.

@AndrewMedico Indeed. And the 787 and A350 aren't on the list. For that matter, neither are the 747 or A380.

The latest types! From this link for the worldwide commercial jet fleet:

shows that jet airliner accidents/million departures declined rapidly from an initial high rate, followed by a slow steady decline to the present day. Experience with the accidents that did happen was built into later production aircraft, and each generation became safer and safer.

Page 19 (Hull loss accident rate per million departures) re-sorted from most to least frequent shows that:

The Really Old Types (no longer in service) and the B707 and DC-8 have the highest accident rate.
The F-28 has a relatively high accident rate: it found a niche in parts of the world with a poor safety record and oversight.
Each subsequent generation of 737 becomes safer.
The most frequent aircraft, B737-NG and A320 family, are amongst the safest.
Of the aircraft with > 1m departures, nobody ever died on board of an A340, B717, or CRJ series. However, fleet size and years in operation have them in the low millions of departures and therefore low statistical significance.
There are 6 types with zero accidents working on their 1 million departure milestone. Aviation is very safe: only after a couple of million of departures of the type do we have significant comparison numbers.

The hull loss chart is inaccurate and statistically skewed in favor of new airplanes. The B747 is one of the safest production aircraft every built but the graph appears to show older planes unsafe - this is not the case. Wiki describes B747 hull loss statistics like this, "Had these planes been newer it would have been economically viable to repair them". Companies are quick (not necessarily involved in serious accidents)  to file insurance claims on older aircraft. https://en.wikipedia.org/wiki/Boeing_747_hull_losses

The hull loss chart also adds a bias between pilot error and aircraft design. Ignoring computerization and improved cockpit design, pilot training has improved; especially in regard to CRM (crew resource management) . CRM has made significant strides in eliminating type A personalities in the cockpit. Which was quite common with the now retired WWII and Vietnam pilots. A crash 30yrs ago is much less likely to result in death today; simply due to pilot training.

@jwzumwalt The document is from the Boeing company - are you saying they skew against their own aircraft? And yes experience is added in all fields in order to improve safety, in construction, piloting, air traffic control...

@jwzumwalt Do you have a link for "type A personality", maybe even one discussing the different personality "types" thus enumerated?

It's not hard, just google 'type a personality'... "Type A and Type B personality theory describes two contrasting personality types. In this theory, personalities that are more competitive, highly organized, ambitious, impatient, highly aware of time management and/or aggressive are labeled Type A, while more relaxed personalities are labeled Type B." - https://en.wikipedia.org/wiki/Type_A_and_Type_B_personality_theory

@ Koyovis - I am saying the use of the data for this discussion is misleading (misapplied). It is one thing to talk about insurance claims and another to attribute that data to aircraft design safety. If you compared the same data with C-172 VS Cyrus, it would look like the C-172 had killed 100,000 people left & right. Actually despite its age, the C172 is a safer airplane. Without careful quantifying a B737 will look much more dangerous than B747 or A380. However 737 are often flown for short hops, short gravel strips and mountainous areas. The flight regime is significant to accident rates.

@jwzumwalt And that is why I'm plotting accident rates: accidents per million departures.

@ Koyovi Without any other data scrubbing, at a minimum it should be per passenger mile, in which case I think the B747 and possibly the A380 would be at least the top 3 or 4. To be accurate accidents such as Tenerife and Colgan should be excluded - these accidents had absolutely nothing to do with aircraft design. That's like blaming gun and car mfg for the deaths of drunks and murders.

@jwzumwalt You're entitled to your opinion of course. Most accidents happen around the runway, cruise is the safest part of the flight, and long range large airliners will have better safety numbers per passenger mile. So if you wish to make a point that the B747 is very safe, you would definitely want to use accidents per passenger mile. But if there is an accident in a large airliner, there are a lot of casualties, so all being equal they should be Included. Pilot error per type probably favours the large types too. In statistics any point can be made if the data is picked carefully.

The chart used is misleading. There have been multiple hull losses and fatalities for both the Bombardier CRJ100 and CRJ200. It is only the CRJ700, CRJ900, and CRJ1000 that have not had a hull loss or fatality.

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text:
What counts as "night" for a student pilot's night landings?
According to 14 CFR 61.57, "no person may act as PIC of an aircraft carrying passengers during the period beginning one hour after sunset and ending one hour before sunrise as published in the American Air Almanac unless, within the preceding 90 days, they have made at least 3 takeoffs and landings to a full stop during that period."
But the definition of nighttime is "the time between the end of evening civil twilight and the beginning of morning civil twilight." (CFR 1.1)
So, when exactly does a student pilot for a PPL complete their night time landings? Do I go off of one hour after sunset time or "official nighttime" time?

The private pilot night requirements are in 61.109, so you should check there rather than 61.57. Although it’s definitely good to know what 61.57 says because that could easily come up during your checkride.

@757toga The reason I think it's a dupe is that the currently accepted (and very good) answer to the linked question covers "Aeronautical Experience Requirement". That's exactly what 61.109 is, and what I understand the OP is asking about. 61.57 doesn't apply to student pilots because they can't carry passengers, although it does become relevant as soon as they become private pilots and it is important to know about. As you said too, the OP shouldn't apply the 61.57 wording to 61.109.

@757toga Totally agree, and that's why I upvoted your answer and downvoted the OP's self-answer :) The OP and others may not see or agree with the distinction that you and I are both making, and I guess that's just how it works out sometimes on StackExchange.

I figured it out actually. Night time flying hours can be logged between evening and morning civil twilights. However, the takeoffs/landings must be between one hour after sunset and one hour before sunrise.
This site makes it clear: https://www.boldmethod.com/learn-to-fly/regulations/logging-night-time-and-night-landings-explained-2021/

This is a good answer, and would be worth migrating to the duplicated question if this one gets closed-as-duplicate.

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text:
Has any commercial airliner ever flown inverted?
Has any commercial airliner ever flown inverted, either intentionally (extremely unlikely) or during an upset?

(I know that the linked question does not ask the same question, but the first answer is a commercial airliner so it still answers your question)

There was a flight a good while ago that had (IIRC) and engine explosion that crippled most of the controls, and inverted was the only way the airplane would fly -- they flipped upright again just before crashing, with some survivors.

In 2018, an employee out of SeaTac stole a Q400 and did a number of aerobatic maneuvers before crashing warning, possibly disturbing/language.

FedEx Flight 705, a DC-10-30 cargo plane, flew at 140 degrees (40 deg off being level inverted) after an attempted hijacking. The FO, Jim Tucker, flew the plane inverted to attempt to throw the would-be hijacker off-balance. The hi-jacker was dead-legging, and was worried that he was about to be sacked by FedEx.

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text:
What were the rules about night flights from LHR in the 80s?
I was just reading a question over on movies.SE: How could Ryan land in New York in early morning?, and the accepted answer suggests that Jack Ryan's plane takes off from LHR at about 4am.
One of the comments on the accepted answer says:

...there are no mid-night commercial flights from any commercial airport (especially LHR) due to night-time noise restrictions...

But were there at the time the film is set?
The film is "The Hunt for Red October", which is apparently set in 1984.
So, I did some searching, and found the following:

Heathrow does still allow a limited number of night landings, but that takeoffs aren't allowed before 6am.
There were court cases in the 90s and early 2000s about the noise caused by night operations at LHR. See this ECHR case from 2001.
An obituary for John Stewart, an anti-noise campaigner, which mentions noise (but not night flights) in the 70s, and the narrowly-lost ECHR court case.
This article about Dan Air, which talks about, in 1982, "...flights to Eilat in Israel. The late night flights, [...] departing from Gatwick". Obviously, that's Israel, not America, and Gatwick, not Heathrow, but it's the right era.

So, my question is this:
During the mid-80s, were there scheduled night flights from Heathrow to the US East Coast, such that Jack Ryan could plausibly have caught one at about 4am, were he not fictional?


text:
Has a plane ever run out of fuel while taxiing?
When planning a flight, the pilots calculate the fuel load, allowing for diversions, delays, etc. While listening to an ATC recording of 30 minute taxi times at JFK, I wondered whether a plane has ever completely run out of fuel while taxiing.
I suspect that it probably would be after arrival, because before take-off, the plane has plenty of fuel.
I'm not talking about running out of fuel in flight: obligatory Gimli Glider link.
I'm aware that at least one Concorde flight landed on fumes, but I think it still made it to the gate.
I found this United Airlines flight from August 2022, which was pre-takeoff: in that case, after 3 hours, the plane returned to the gate to refuel, and then taxied for another few hours before the flight was finally cancelled.
I'm looking for more extreme instances of that story:
Has a commercial transport plane ever completely run out of fuel while taxiing?

If before takeoff, that would be a very lucky crew. There was an instance in the Navy where the refulers only topped off the wing tanks in an F-4 Phantom, and since the Squat Switch (which indicates that the aircraft is on the ground) inhibits pressurization of those tanks, no fuel could transfer into the main fuselage feed tank until they took off.  Since they were only flying a few miles, the fuel in the wing tanks was enough to get where they were going, so the pilot decided to just takeoff, and let the wing tank fuel transfer then. The engines flamed out shortly after they got airborne.

I can envision the pilot coming on the intercom: "OK, folks, this is embarrassing, but we've run out of gas. I'm going to need everybody out to help push us to the the next taxiway turnoff while the copilot goes to the station with the company credit card to pick up a couple of gallons..."

I take the question here to really mean "taxiing before takeoff". Because if planes can run out of fuel while in the air (Gimli glider of course, but many more over the years) then I imagine there have been some situations, perhaps with lots of weather delays or in wartime, where a plane had just barely enough fuel to keep the engines running through landing and then got stuck on the runway (or a taxiway) because they ran out of fuel right after landing.

"then got stuck on the runway (or a taxiway) because they ran out of fuel right after landing" -- I've updated; I suspect that this would be more common. I'm looking for cases where (e.g. due to taxiway congestion) the pilot's had to make a sheepish announcement over the PA.

Even if an aircraft landed on fumes, one would think that they'd simply shut down and call for a tow before letting the airplane actually get to the point of fuel starvation. Though, if one is landing with that little fuel, it should already be an emergency flight receiving priority handling anyway.

wait -  regarding waiting to take off isn't it commonplace that (due to some extreme delay) an airliner has to give up, and go back and fuel-up?  No?  Perhaps I'm wrong

You already referenced the United Airlines incident and that should be as close as it ever gets. To physically run out of fuel "while taxiing", the Pilot in Command and Pilot Monitoring must have completely ignored the gauges and botched the pre-flight checks since they clearly would not have enough fuel to make their destination or an alternate landing. Any crew in that position should be immediately de-registered, terminated and their licenses pulled

@Fattie: Sure, but they need to refuel after a takeoff delay so they'll have enough gas to make it to the destination after takeoff (plus reserves etc).  Not to avoid running out of gas before they even take off.

@PeterCordes - right, it was just a little unclear what the OP was asking ...

I saw this happen one time. A DC-3 pulled up to a flight school's pump because no one else had gas. The flight line kid dutifully pumped x gallons into the tanks, but didn't verify with the dipstick. Pilot was in a hurry and also did not verify. Turns out the pump was dry but also faulty and did not stop when it ran out of gas. Then the DC-3 taxiied out, and before takeoff it did run out of gas.

Lucky pilot. That could have gone a lot worse.

Solid argument for a refund there.

@MadPhysicist

Is there an NTSB report on this incident you could link to?

No idea. This happened in the mid-1970's. There was no incident or accident. One engine shut down on run up, so they shut down the other one once they realized why and towed it back to the line. It wasn't a scheduled flight, I think the pilot was just repositioning the aircraft to another field for/after maintenance. I doubt anyone bothered to report it.

One would really, really hope not, although "ever in recorded history" includes a lot of cases.
Fuel burn while taxiing is considerably less than during flight, by a factor maybe 4 or 5 (for a 737) with both engines running, and a factor of over 10 with engines shut down & just the APU running. So even with just barely enough gas for a 1-hour flight plus min reserves, that's still a lot of taxi time. And at some point, one would think that the crew (or their dispatcher) would realize that they have too little gas to legally take off, so they need to go back to the gate.
Of course, there are circumstances one can imagine that might prevent the aircraft from returning to the gate to refuel, and maybe there has been a case where they burned all their gas waiting to return but not being able to: a really bad blizzard, some sort of accident blocking the taxi route to the gates, a 9/11 type of shut-down, and the gridlock that these sorts of events could cause might do it.
But, while it's hard to "prove a negative," I've not heard of such a incident.

"circumstances one can imagine that might prevent the aircraft from returning to the gate to refuel" -- yeah; this is the crux of my question. Also: I can't imagine the hell of being stuck on a taxiing plane for longer than it takes to fly to the destination and back.

Yeah, that would be a really, really unpleasant day, for sure! These days, airlines get immense fines for over 3 hours on the tarmac (longer for international), so it's a priority (which ATC understands) to get either to a gate or off the ground sooner than that. Before that rule, and in places not under FAA jurisdiction, things can drag out pretty badly, especially waiting on Customs to show up (i.e. after a landing or diversion).  So it's not completely inconceivable it could have happened somewhere, some time. Not aware of where/when, though.

Technically, a plane that catches fire for whatever reason and burns off all its fuel while taxiing would "run out of fuel".  Based on this, the answer to the title question must be Yes.

@RogerLipscombe I can't imagine the hell of being stuck on a taxiing plane for longer than it takes to fly to the destination and back - I can. About 20 years ago I was flying from Boston, MA (BOS) to Washington Dulles (IAD), which is normally just over an hour and a half. Due to a really bad blizzard in Boston, we were stuck on taxiways for nearly 4 hours before returning to the gate to refuel and then taking off another 1 hour later.


text:
Isn't it time the aviation sector improve its policies
In spite of the strict rules and regulations we see many disasters taking place. Mostly the disaster occurs due to the lapse of one small policy or nature. If the policy is the best then why do crashes still take place.
If one jet meets a disaster only then other's follow suite regarding their policies(modification or updating it). Is it necessary for a plane to crash for the improvement of the aviation sector can't we hope for a zero crash year.
At first it's the MH series crashing and now recently one more from Algeria bound plane and later a training helicopter.
This year the aviation sector has made several people to think twice before they travel or they might end up in tragedy

let me put it this way: how often do planes crash? How often do buses crash?

@JanDvorak its like comparing prop engine with a jet, Do you get chances of survival mid air or on the ground

it's rarely just one thing that fails but a sequence of events that cooperate into a crash

@user285oo6 Planes-vs-Buses is a perfectly apt comparison: We kill many more people per passenger-mile on the roads than we do in the air every year, yet people don't "think twice" before getting in their car every morning to drive to work. Does the automobile/driving "industry" need to improve its policies to address their fatal accident rate?

"At first it's the MH series crashing" - not the first fatal accident this year. "can't we hope for a zero crash year" - we had one already, 1932.

@AakashM So you are agreeing that aviation is not safe anymore by saying only 1932 the year of 0 crash(not near 2000 atleast) and  for the MH which crashed in Inidian ocean we didn't get the Black box till now to avoid this in future.

Maybe, just maybe, it's not as simple as 'safe' versus 'not safe' ?

@user285oo6 Can you name the year where we had 'zero' kills on roads? That would most likely be the years before cars were invented...

@SentryRaven more likely the years before roads were invented.

In spite of the strict rules and regulations we see many disasters taking place.

Do we?
In the last month or so we've seen several major aircraft accidents/incidents worldwide resulting in loss of hundreds of lives.
However in that same time we've probably seen tens or hundreds of thousands die from other accidental causes. For example in one small typical western country there are 17,000 accidental deaths each year 2,000 deaths from transport accidents and 140,000 deaths from cancer.
 - Cancer                     140000
 - Transport Accidents          2000
 - Air accidents                  20

 W.H.O.
Look, road injury: 1.3 million deaths each year.
In a rational society, this should have some weight in guiding where we ask our governments to spend our money and resources.

Is it necessary for a plane to crash for the improvement of the aviation sector

Yes, to an extent. We the public only pay attention when these things are reported in the mass media, the rest of the time we demand cheap air fares and push out of business any airline that spends much more than the average on safety.

This isn't to argue that we should be complacent, in fact hundreds of people will spend months and years investigating each of those air accidents.

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text:
Why does the Boeing 737 have 5 x the passenger fatalities of the Airbus 320?
I thought I'd compare the accident rates of these two similar, competing, very successful aircraft.
                    737     A320

Introduced          1968    1988
Number Built        8104    6171
Accidents/Incidents  329      60
Hull Loss Accidents  154      23
Fatalities          4287     782

These figures are from the respective Wikipedia pages. I assume they have not been the subject of edit-war falsification by fanboys of planemakers.
I wondered what might be the reason for the 737 seeming a much less safe plane.

The 737 design is 20 years older?

But it's still in production, so 1988...current 737s can be built with many of the same safety features found in an A320 produced the same year. Were 3,500 of those fatalities in the first 20 years?

There are lots more older less-safe 737s being flown by corner-cutting budget airlines in third-world kleptocracies?

Are there that many 40-year old 737s in the hands of incompetent airlines?

The 8,104 737s have, on average, flown many times more cycles than the 6,171 A320s?

But they address the same market, why would their usage differ so markedly?

The 737s have, together, flown many times more passenger-miles than the A320s?

See above. Plus I imagine older 737s have mostly been retired.

My speculation doesn't seem very convincing to me. Is there a better explanation supported by reputable studies?

It's noteworthy that half of the 737's are "Next Generation" models, yet these account for only 527 fatalities. The remaining 3760 fatalities were in earlier models. Of course, these planes have flown more miles, so the difference in fatalities per passenger-mile is most likely lower than 5x.

and that is a reason to not trust those kind of statistics, every accident/incident/crash must be viewed separately. Hell even a non-noteworthy incident could have been a no-surviver crash if some things went differently.

Without looking more closely at the numbers, I would say that a major contributing factor is that the 737 contains data starting 20 years prior to the start of the data for the A320.  Aviation progressed a long ways in those 20 years by developing safe practices all across the industry which helped to lower the accident rate for everyone.

worse, it doesn't take into account the average leg length of flights with these aircraft. Many 737s are used for things like island hopping and other very high rotation jobs, and with accidents more likely to happen during takeoff and landing are therefore more "at risk" than aircraft that tend to fly longer hops.

"See above. Plus I imagine older 737s have mostly been retired".  Take a trip to Central and South America.  You'll find plenty of the old 737 in service and being scrapped for parts to keep the other old ones in the air.

At an educated guess it’s due to 737s operating in an earlier age of air travel where the accident rates were a lot higher than that of later eras in which the A320 series operates in.  The Airbus model benefited from the 20 or so years of lessons learned in air travel prior to its introduction.

For one, the early 737s had a design flaw which allowed the rudder to reach a hard-over position, and get stuck there. Boeing initially dragged their feet in rectifying this, so it took a number of accidents before this design flaw was corrected. This is a major contributor to the high number of fatalities in the early operational years.
To have a more meaningful comparison, I would suggest to compare the fatalities per year, so the status in operational procedures can be excluded as a factor. As others have pointed out, this should give a more equal basis for a comparison.
If you look at fatalities per year, beginning in 2000, these numbers emerge:

Now you need to factor in the number of flight hours per type per year, which I do not have available. But I would expect that the low fatality rate in the early 2000s is more due to the small number of A320s around. But if we just compare the 737 NG with the A320, this advantage is reversed, and still the A320 comes out slightly ahead.
But thankfully, there are very few accidents for each type per year, so the statistical base is too low for a meaningful comparison. If we want to draw any conclusions, it could be that the A320 is indeed a safer aircraft, but the certainty of this conclusion is very low, being based on a very small number of accidents.

Well, to be fair, the difference between the NGs and the A320 here would be well within the margin of error. A single incident would likely flip which one had more fatalities. And, in fact, according to your numbers here, it was the other way around as of the end of 2009. I doubt that which airframe is more safe has really changed since then.

@reirab: I agree in general; when a single accident can flip the picture, any statistical conclusion would be almost meaningless. But you need to consider that many more A-320 were flying at the time than 737 NGs, and if you take that into consideration, the A-320 could well be considered safer even in the time before 2009 - with all caveats, as mentioned above.

+1 for the last part of the answer. This is a really rare event, and statistic over such low rate are not relevant.

Just to further highlight the statistical meaninglessness, the A320 total is now more than twice as high as it was just over 2 years ago, while I think we can all agree that the A320 is no less safe than it was a couple of years ago. The 777 highlights this even more. Until summer 2013, there had been a grand total of zero passenger deaths on a 777 ever (in nearly 20 years of operational history,) then 3 fatal incidents happened within a year (none of which, as far as we know, were actually related to the airframe.)

We simply need more accidents to collect statistical data. /sarcasm

That table has at least two errors; the total number of 737NG fatalities for 2007 should read 114, not 113, and the total number of A320 fatalities for that year should read 187, not 186.

Also, is the A320 column supposed to be for just the A320 itself, or for the entire A320 family?  If the latter, its entry for 2010 should be 152, not 0.

Raw numbers like this are more-or-less useless. You would have to plot the accidents against the year to even begin to have something reasonable. You also need to remove non-airframe accidents like:

under-full-control crashes like controlled flight into terrain (pilot screwups have nothing to do with the airframe, and account for a lot of accidents)
weather-related issues that are not pilot screwups (e.g. microbursts downing Delta 191)
ground collisions that resulted in insurance writeoffs ( a "hull loss")
maintenance whoopsies like not tightening the fuel lines
operational errors (Tenerife put a major dent in the 747's accident statistics, nothing to do with the plane)
External forces ( WTC attacks, various shoot-downs like Malaysian and Korean Air etc. )

Once you look at 3rd-owner and beyond you may find yourself in the less developed countries with poor maintenance, training etc. and then it gets a lot harder. It's even tricky with first-line carriers. Was Aloha Airlines Flight 243 (the Sunshine Roof flight) a design flaw, maintenance not fixing it properly, operations not grounding it for maintenace etc. etc.

@Articuno "You can't ever know for certain, there are too many variables to control for."

Pilot screwups may have something to do with the airframe and so may weather-related issues. The flight envelope protection of A320 does help sometimes.

Are you saying that Airbus pilots make fewer screwups, avoid weather, don't hit things on the ground, have more careful groundcrew & engineers, get better ATC instructions and are less favoured by terrorists?  I'd expect little or no difference.

Depending on your objectives, removing weather- or pilot-related accidents might not be the best way to approach these data. Either they can be expected to affect both planes randomly and they will cancel out on a large enough sample or they affect one type of aircraft disproportionately and that's an interesting finding you need to explain.

@RedGrittyBrick I'm saying you have to REMOVE the pilot error, weather etc. from the numbers. Not explain them as a result of the numbers.

@dotancohen: Tenerife was 100% pilot error. "if they had used a smaller plane" might have prevented that particular accident at the expense of another somewhere else. Your statement is rewriting history to achieve a particular outcome.

@Paul: I don't understand what you mean. Please explain. If 737s have 5x the fatalities largely because they encounter 5x more microbursts - that would answer my question wouldn't it?

The problem with this answer us that it skews the problem even further. If you remove similar amounts of type-independent crashes, the ratio of the remaining crashes will shift up even more. In other word, excluding external causes, why are there 6-7x more fatalities in a 737?

@MSalters That makes at least the very big assumption that pilot errors, weather incidents, etc. were constant the whole time. It seems not that unreasonable to assume that stricter regulations, maintenance rules, etc. would influence the rate (and hopefully lower it in later years).

@RedGrittyBrick 737s will not encounter 5x more microbursts as they are a random phenomenon. Today we have doppler weather radar that will tell us plane-downing microbursts are likely and we avoid that area. This technology has existed for 100% of the A320 career but only half of the 737's. Therefore you must exclude suspected microburst crashes from the 737 numbers before 1988 or your results will be largely meaningless.

@Relaxed The problem with that is that we don't actually have a large enough sample. Airliner crashes are so incredibly rare that 1 or 2 accidents/incidents can dramatically change the number of passenger deaths for the type. Consider the 777, for example. Just last year, its passenger death total went from 2 (or 3 if you count the one hit by a fire truck at SFO) to 527 (or 528.) Just over 2 years ago, its total was zero. The A320 has had a similarly bad year since this question was written (German Wings and AirAsia crashes.)

@reirab Obviously but that's mostly unrelated to my point.

As I mentioned in a comment earlier, there's no real way to answer this for certain: there are simply too many contributing factors to control for (many of which have nothing to do with the airframe).
Broadly speaking I suspect the 20 years more service time, much of it back when aviation accidents were somewhat more common, is a large part of it.  Boeing has a great presentation covering the commercial fleet accident rate from 1959-2012, and just looking at the accident rate graph shows how far commercial air travel has come in cutting their accident rate.
That being said while I do enjoy mercilessly mocking Airbus aircraft the A320 series has an enviable safety record, and certainly some part of that can be credited to the airframe and crew training programs in addition to the broader safety improvements in commercial aviation - just don't ask me to be specific as to how much...

@RedGrittyBrick I knew it existed but Google found it for me (I don't recall my search string, but "Boeing statistical summary of commercial jet airplane accidents" is apparently what it's officially called). A new one should be coming out right about now, and SKYbrary.aero has historical ones which are interesting for the "current" event details.

The link actually has the answer. Hull loss rate/million departures: 737-1/200: 1.75, 737-3/4/500: 0.52, 737-6/7/8/900: 0.26, A318-A321: 0.26. The old 737s are 7 times less safe.

@MSalters Drawing that conclusion ignores the fact that the general accident rate was substantially higher pre-1984 (when the 737-300 hit the market). There are many factors contributing to the decline in accidents, many of them completely unrelated to the airframes in service, and to simply state that the older airframes are "7 times less safe" ignores every other contributing factor. It's like saying the 737 is "5 times less safe" than the A380 based on the raw numbers in the question...

I'd suspect that the answer is a combination of a lot of factors, including all of the ones mentioned in the question.

•There are lots more older less-safe 737s being flown by corner-cutting budget airlines in third-world kleptocracies?

•Are there that many 40-year old 737s in the hands of incompetent airlines?

In short, yes. They might not all be 40 years old, but, yes, there are tons of older 737s that were sold off to third-world airlines and/or airlines that simply operate in more dangerous areas. It's probably the single most common jet airliner in such situations.

•The 8,104 737s have, on average, flown many times more cycles than the 6,171 A320s?

•But they address the same market, why would their usage differ so markedly?

While I'm not sure that their average use cases are very different for aircraft of the same age, there are far more old 737s than old A320s. A lot of the 737 fleet already had flown many cycles before the first A320 ever rolled out of the factory. The average 737 is significantly older than the average A320 and, thus, has flown more flight cycles. While the first A320 delivery was in 1988, the vast majority of A320 deliveries have been since 2000 (5,029 A320s out of 6,171 in service were delivered 2000 or later.) Based on their respective Wikipedia Orders and Deliveries numbers by year, the average fleet age of the 737 is a little over 16 years while the average age of A320s is only about 8.5 years. Of course, this also means that there are a lot more old 737s to be sold to the aforementioned third-world airlines than A320s.

•The 737s have, together, flown many times more passenger-miles than the A320s?

•See above. Plus I imagine older 737s have mostly been retired.

In addition to the average 737 being significantly older (and, thus, having significantly more flight-cycles) than the average A320, you still have to consider that there are 31% more delivered 737s than A320s. In total, the B737 fleet has about 131,000 aircraft-years of history compared to about 52,800 aircraft-years for the A320. So, aircraft-years of service alone explains a factor of 2.5 (half the difference.)

So, in short, I don't think any one factor explains the difference, but the sum of several factors, most of them being related to age, does explain the difference.

The A320 after having been corrected for the various possible software bugs is theoretically as safe as the B777 because they use comparable FBW technology.
Technically you cannot compare the A320 to the B737 because they are technically totally different even though competing commercially.
The safety of the A320 relies on the automatic checklist like the B777, on the FBW, on the redundancies  as a summary on Technology
The safety of the B737 relies on the experienced pilots from generation to generation who know all its qualities but also all its weaknesses
June 18, 2019
As a further justification, for instance on the 737max the pilots did loose precious time fetching in the paper checklist the appropriate action to do, while with an automatic checklist like on the B777 or the A320 they wouldn’t have crashed.

Just because an A320 has more advanced technology, that hardly implies you don't need an experienced pilot to fly it. Similarly, the 737 also relies on various technologies and redundancies to improve safety. It is a different concept, but all aircraft require good systems and a good pilot to fly safely.

@Bianfable, what you are stating is the Bible of aviation, and everybody does agree; what I am indicating are features that are more necessary to this or to that aircraft, for instance on the max the pilots did loose time fetching in the paper checklist the appropriate action to do, while with an automatic checklist like on the B777 or the A320 they wouldn’t have crashes

A320 has triple redundancy in systems like AOA and radio altimeter/ autoland vs Boeing double radio altimeter/ autoland and single aoa channel. Design philosophy and cost savings approach seems more safety oriented on the airbus.


text:
Received ADS-B TC=31 message with non-existent version 3?
On several dates, my ground station received some airborne operational status ADS-B messages (TC=31) where the version number was reported as 3. As far as I know, the only valid versions are 0, 1, and 2.
I don't think it was just a garbled reception because

I received more than 500 messages of the same type, all reporting 3 as the version number.
The messages came from three USAF aircraft of the same type, KC-10A Extenders.

Here is a sample message, in raw form: 8DAE022EF8000000206143635C24
The dates on which I saw the messages:

2018-04-13
2019-02-16

The aircraft associated with the messages:

ICAO AE020E, registration 79-1948
ICAO AE0212, registration 82-0193
ICAO AE022E, registration 86-0037

What's the most likely reason behind these messages having this (AFAIK non-existent) version number? A test? A misconfigured piece of equipment (it strikes me as unlikely that the version number can be set to 3, but maybe I'm wrong). Is it a bug in the decoder I'm using?
[Edited 2019-02-16 to include other aircraft I've received the anomalous messages from.]

When you receive these messages, do you receive a steady stream of other messages from the same 24 bit address?

BTW: these aircraft appear to be Travis AFB based aircraft from markings in available photos (60AMW, to be precise).  I poked the wing through the contact form on the Travis AFB website, requesting a reply, and will respond if/when I get one.

Please, can you explain me what is MOPS , dose it we from transponder and Ground Station , and what is his relationship with quality indicator

I've decoded the message with my own decoder. I don't claim it is bug free, but it is designed to follow the 1090ES MOPS (ADS-B Minimum Operational Performance Standards) very closely and gives warnings when messages deviate from the standard. I forced decoding conforming to version 2 of the MOPS, which is the latest standard.
HEX: 8DAE022EF8000000206143635C24
Aircraft Operational status message (airborne format)
    Capability Class:
        TCAS op.          false
        1090ES IN         false
        Reserved [13,14]      0
        ARV rep. cap.     false
        TS report cap.    false
        TC rep. cap. lvl      0
        UAT IN            false
        ADS-R rsvd flag   false
        Reserved              0
    Airborne Operational Mode (OM)
        TCAS RA active    false
        IDENT             false
        Reserved [ATC]    false
        Single Antenna    false
        SDA               0
        Reserved [33-40]  32
     MOPS version     3
     NIC supp. A      false
     NACp             1
     GVA              1
     SIL              0
     SIL supp.        true
     NIC baro         0
     Heading ref.     True North
     Reserved [56]    true

The 1090ES MOPS version is indeed indicated as version 3, which is not yet published.
Also, the ME-bits 35 and 56 are set to 1. In version 2 of the 1090ES MOPS these are reserved bits, so they shall be 0.
Version 3 of the 1090ES MOPS is not yet published, so transponders should not use it.
Perhaps these messages are from an experimental transponder, which does not conform to the MOPS.

Transponders with ICAO addresses AE* are usually those used in military planes. Military planes often tamper with the payload of the transmissions. My guess is that they set the version to 3 to make sure that any receiver following the specifications ignores these transmissions.

In addition, there's no way to know how to decode the message correctly. From version 0 to 1/2, the format of operational status messages changed entirely which might also happen in version 3.

According to the FAA's Advisory Circular AC20-165B, numbers higher than 2 are allowed:

A.2.34 Version Number.
The applicable TSO Minimum Operational Performance Standard (MOPS)
  level is communicated through the version number, which is fixed at
  the time the ADS-B equipment is manufactured. Version 2 applies to
  ADS-B equipment that meets MOPS documents RTCA/DO-260B with
  corrigendum 1 or RTCA/DO-282B with corrigendum
  1. ADS-B equipment outputting version 2 or higher is required by § 91.227.

Version 3 ADS-B Out avionics meet the requirements defined in DO-260C or DO-282C; although since you are referring to operational status messages my guess is that you are talking about 1090ES messages (i.e. compliant with DO-260C).

But DO-260C is not yet published :-)

Working on it ;)


text:
What is the significance of a clover-shaped flight track?
These are portions of two flights by a Cessna T206H on separate days:

The cloverleaf portion of the track was flown at around 8200 feet altitude. This plane is typically seen over the Los Angeles basin flying "lawnmower" patterns similar to those that might be used for sterile insect technique flights or aerial imagery collection flights.
What is the significance of this pattern?  Could it be for radio direction finding?
Edit: The aircraft is N915WC, which is registered to a company that specializes in supporting the intelligence community and law enforcement.  I didn't mention that initially because I didn't want to bias people's answers, and I was curious if the pattern was distinctive enough to identify without that information.

Take a look at https://www.flightradar24.com/blog/interesting-patterns-on-flightradar24/ and https://www.flightradar24.com/blog/how-to-draw-a-plane-with-a-plane/ too

@SMSvonderTann Whoever did that drawing of the airplane has some mad skills!

Might be for aerial photography or something but I don't see anything on Google earth that looks particularly interesting there. On the sectional right at that spot is an info box saying "Caution, intensive flight training below 4500'"

Looks like flight training to me.

Someone taking a friend to look at their house, then their neighbour hearing about it and asking if they can have a go, too? :p

This is probably fodder for a new question, but I've got to assume that the sharp angles in those tracks are just glitches in the trace, not the plane actually making a tight turn at that location. Is that correct?

Yup, looks like some shaky beginner work from flower guy.

A 206 isn't a typical civilian training aircraft but one possibility is the Civil Air Patrol. They have some 206s and the track looks a little like a sector search pattern so it could be a training exercise. But that's a complete guess, it could also be the FBI or another organization. If you have the N number then you could research that (how do you know it's a 206?).

That Visual Search Patterns chapter is really interesting, thanks.  The aircraft I'm asking about is N915WC, owned by a defense contractor involved in lots of different activities--including mapping and surveillance.  I left that out of my question because I was curious if the track itself was distinctive enough and didn't want to bias people's answers.

The "metered search" pattern described in "Electronic Search Patterns", used for determining the location of an ELT (or other radio signal?), looks a little similar.

The flying looks too sloppy for a ground reference maneuver, a performance maneuver, or other required academic flying.  Given the concentration of the same flying in that same area and a review of the VFR sectional for the same area:

This is probably some kind of training flight.  If it is for law enforcement, I'm not sure what is going on here.  One possibility is that it is a student practicing attitude instrument flying doing 'A' and 'B' patterns under the hood with an instructor - or at least trying to.

Another possibility is just standard flight training activities, periodically turning to avoid terrain or congested airspace in order to operate within these confines.

That just looks to me like someone was practicing holding patterns, and the second pic seems to also show turns around a point. Could be flight training, a BFR, whatever.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

Neither is that an informed review. If you are not a pilot, please refrain from commenting on this. That is an appropriate answer given the very limited information provided.


text:
In what circumstances could a 787 stay powered on continuously for 248 days?
The FAA has issued an airworthiness directive for the 787:

SUMMARY: We are adopting a new airworthiness directive (AD) for all
  The Boeing Company Model 787 airplanes. This AD requires a repetitive
  maintenance task for electrical power deactivation on Model 787
  airplanes. This AD was prompted by the determination that a Model 787
  airplane that has been powered continuously for 248 days can lose all
  alternating current (AC) electrical power due to the generator control
  units (GCUs) simultaneously going into failsafe mode. This condition
  is caused by a software counter internal to the GCUs that will
  overflow after 248 days of continuous power. We are issuing this AD to
  prevent loss of all AC electrical power, which could result in loss of
  control of the airplane.

I'm curious: Are there any circumstances under which a 787 would remain powered continuously for 248 days?
[Edited to add a follow-on question:]
Boeing has said "If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required."  Does that happen? 120 days?
What is the longest period a passenger aircraft might conceivably be continuously powered on?

2147483648 centiseconds = 248.55 days (now we know they're using signed 32-bit integers........)

@kevin Or unsigned 32-bit integers with a timer interrupt period of 5 milliseconds. :)

"Ladies and gentlemen, may I have your attention, please? Our captain has just informed me that our aircraft is scheduled to undergo a normal, scheduled maintenance procedure known as 'rebooting'. During this procedure you may notice the engines shut down, the wind noise outside the aircraft increases in volume and frequency, and shouts of 'Oh my god! Oh my god! We're all gonna die!!' may emanate from the vicinity of the cockpit. Please rest assured that this is all totally normal and under control. And thank you for flying in our Boeing 787 today - now powered by Microsoft Windows..." :-)

On a more instructive note, I find it interesting that there are 21427200 seconds in 248 days. If the operating software of the plane measures time in 1/100ths of a second then it would overflow a 32 bit signed integer time field after about 248 days, 13 hours, and fourteen minutes. I don't know if this is the actual problem but A) it's certainly coincidental that the timespan-to-overflow under this assumption is so close, and B) that the Patriot missile batteries used in the first Gulf War suffered from a similar overflow problem. Boeing's mileage may vary...

@BobJarvis: Wouldn't the wind noise decrease in volume and frequency with the engines shut down (due to the plane slowing down from aerodynamic drag)?

Aircrews seldom have to power off an aircraft completely (also known as a cold and dark cockpit). Airliners usually stay powered on at the gate. This is known as a "short turn-around": engines are stopped, the APU is stopped, but electrical power and air conditioning is still supplied by ground equipment.
This has the advantage of minimizing turn-around time (after all, airliners are meant to stay in the air to make money). The cabin also has to be cleaned and prepared for the next flight at this time, so something must power the lights.
It is theoretically possible to stay on this way for 248 days. However, airliners have scheduled maintenance, which completely powers off the aircraft. They are also powered off if the expected time at the gate is long. So, in reality, it's very unlikely to have an airliner powered continuously for 248 days.

I'm guessing you meant to say "Aircrews seldom have to power off an aircraft completely..."?  What are typical scheduled maintenance intervals?

@JohnWiseman the engineers can power off or on aircrafts if necessary. Scheduled maintenance intervals are usually named "A", "B", "C" or "D" checks. "A" is the simplest, performed every 250 flight hours; while "D" is the most comprehensive. For details see http://en.wikipedia.org/wiki/Aircraft_maintenance_checks

There have been issues with the 787 giving "nuisance" messages after starting up. One solution would be to start the process earlier, to leave time to deal with them. Another is to just never shut it down. However, the plane does need to be shut down sometimes for regular maintenance. A Boeing spokesperson said:

No airplane in the fleet experienced that condition.

The issue was discovered during lab testing, and while it would be unusual for a plane to be on for 248 days straight, it's not impossible, so Murphy says that it will occur at the worst possible time. So in the interest of safety, the FAA is making operators aware so that they can be sure to shut down their planes regularly and avoid the issue.

I suppose a response of "have you tried switching your aeroplane off and back on again" wouldn't be considered an appropriate way to deal with these "nuisance" messages.

I've been sitting on a Boeing 757 when they changed the fan tray (presumably in the electronics rack) and the error messages persisted, so "switch it off and back on" is exactly what they did. Takes a surprising time for everything to spin down, but it worked, and off we went. Presumably 757s don't have ctrl, alt, and delete keys!

Why did this answer make me think of Microsoft products?

@BrianTopping Microsoft is headquartered close to where Boeing was founded...

This is a bug Boeing found in the 787. This bug, which was found during laboratory testing, is:

... plane’s power control units could shut down power generators if they were powered without interruption for 248 days, or about eight months

This bug wasn't found in any airplanes in line operations. Boeing states that:

... power was shut down in all airplanes in service in the course of the regular maintenance schedule ...

Airliners stay on for very long times, but their proper maintenance requires them to be power cycled regularly. About this issue, Boeing says:

If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required.

So, the answer to your question is there aren't any.

"So, the answer to your question is there aren't any." If the A check doesn't require power-off, and the B check is done approximately every 180 days (according to @kevin's Wikipedia link above) it would be theoretically possible for Third-World Airlines Inc to "accidentally" file the paperwork for the B check without actually doing it, and trigger the problem. That is very unlikely to be a current problem with a new aircraft type, but 40 years from now some of them will still be flying having been sold on as "pre-owned".

@alephzero: This might be a feature and not a bug for the "accidental file" problem. If it weren't for innocents being involved, it certainly would highlight the problem airlines.

@alephzero: I wonder if a reasonable fix might be to add some code which, if the plain has gone more than 180 days since the last reboot, would start showing a message indicating that the plain must rebooted within the next 60/59/58/etc. days (leaving 8 days' cushion at the end).  I would think two months' notice that the system must be rebooted would be sufficient to ensure that someone would notice.

At an air museum, an employee once told me that software used in commercial airliners undergoes around 10 years of testing before it is deployed.
That's probably why they just issued a policy. Chances are, they'll go to 64-bit (or implement such a warning) in, well, 10 years? :)

@supercat - the more reasonable fix would be to fix the wrapping counter to stop overflowing every 248 days. If they are going to push out a fix, it might as well be a real fix and not a band-aid.

@Johnny: Any change to try to "fix" the problem would either require a really massive amount of work, or would run the risk of leaving some detail overlooked.  If the only way in which the system could be left running for 180+ days continuously would be if other required safety procedures were being ignored, the ability for the software to cope with being left on for 240+ days would not improve the value of the plane to any conscientious airline.  Unless pilots are willing to ignore for two months a message saying the plane should be rebooted when practical, and for another week...

...saying that the plane should not take off until it is rebooted unless takeoff is necessary to avoid an imminent disaster (e.g. the plane is parked near some fuel tanks that might catch fire) adding a message but leaving the software unchanged would probably pose less safety risk than changing the software and not alerting anyone that the plane hasn't been rebooted in nine months.

authors: Bob Jarvis - Слава Україні


text:
Does lift coefficient for maximum range change for a glider experiencing headwind?
When a glider or unpropelled aircraft experiences headwind, I understand that the flight velocity and sink velocity for the "new" maximum possible range both increase (see velocity polar from How does wind affect the airspeed that I should fly for maximum range in an airplane?).

Intuitively I would think this means that $C_{L}$ needs to decrease so that the now higher $\frac{1}{2}\rho v^2$ can be compensated (small glide slope assumption $L \approx G$ i.e. $L >> D$).
For the theoretical $C_{L_{R_{max}}}$ equation for a symmetric $C_{L}-C_{D}$ polar, I don't see this playing a role:
$C_{L_{R_{max}}}=\sqrt{C_{D_0}\pi\Lambda e} $
...as $C_{D_0}$ to my knowledge doesn't change with velocity.
Does lift coefficient $C_{L_{R_{max}}}$ for maximum range change for a glider experiencing headwind?

Your first statement is correct, look at the lift vs AOA chart.  You go faster by pitching down (reducing lift and drag) and speeding up above Vbg(lift recovered now more drag), which effectively changes your trim and lowers AOA.  Why?  Because best gliding "Vbg" is all about covering the most distance per unit altitude, NOT time in the air.
In the most extreme case:  headwind = gliding airspeed you can see that no forward progress is made unless you glide faster.  Forward progress per unit altitude is:
(airspeed - headwind)/altitude
Your new Vbg now factors in ground gain vs increase in parasitic drag.  The result is (obviously) you can't glide as far into a headwind, but (more importantly) you can help making your landing zone in a headwind by increasing your airspeed above published Vbg.

A very experienced glider pilot once told my non believing ears that not only going above Vbg to "get home", but also giving up altitude and "getting low" worked well in a headwind (wind gradient makes gliding lower more efficient).  Technique will vary from plane to plane.

This is what glider pilot mean when they talk about "penetration",

great answer, but what happens to my CA when I fly faster? does it decrease?

@HotDogCannon CA? You get same lift with lower Clift when you fly faster, but parasite drag increases, so total drag increases above Vbg.  You weigh this against headwind effects on gliding distance to get your new headwind condition Vbg.

@RobertDiGiovanni I meant CL... it's CA in the german speaking world ;) I think I understand it a bit better now. CL is simply no longer the CL given by the equation for CL( (CL/CD)max ) in "still air" and must be calculated from the optimal velocity that is calculated by taking into account the reference frame shift between ground / TAS, etc, which gets more complicated, or done graphically using the method in the figure above. In any case, given a headwind, the optimal velocity for max range is higher, meaning my CL is lower for constant lift.

Yes, in a glider with a ground point reference you would pitch down until that point rises in your windscreen the least (or even starts falling) to get headwind Vbg.  Not an exact science as wind will vary.  But even without headwind the concept holds for max distance, which is why maximum time in air (minimum thrust to maintain flight/rate of descent) speed is lower still, right at the top of the curve.  You just don't go as far.